Diffuse optical imaging (“DOI”) is an imaging methodology that can be utilized in mapping the functional activity in the human brain. With unique capabilities that include functional neuroimaging method, DOI complements and expands upon the other more established modalities such as Positron Emission Tomography (“PET”) and Magnetic Resonance Imaging (“MRI”). While tremendously useful, the scanning environments of MRI and PET brain instruments generally require a fixed head placement in an enclosed tube, with significant scanner noise such as that found with MRI or the use of radioactive isotopes such as that found with PET.
In marked contrast to the more expensive scanner based technology (e.g. MRI and PET), DOI employs a less extensive technology platform and a wearable imaging cap. The DOI cap is well suited for several situations that are not amenable to fixed scanner environments, including the ability to obtain images of moving subjects who might otherwise require sedation, unmovable subjects, non-communicative subjects, patients in intensive care, subjects with metal implants, as well as studies of human development in children that would benefit from enriched ecological environments for a wider range of behavioral paradigms. The application that has particularly high potential is the use of DOI for critical care monitoring of infants and neonates.
Diffuse Optical Imaging (“DOI”) builds images out of a number of discrete source and detector pair (“optode-pair”) near-infrared spectroscopic samplings that are made non-invasively. When there is a single point measurement that is utilized without imaging, utilizing one or just a few optode pairs, the technique is referred to as near-infrared spectroscopy (“NIRS”).
Previous diffuse optical neuroimaging systems have utilized sparse imaging arrays such as that disclosed in FIG. 1, which are generally indicated by numeral 10. In this scenario, sources are indicated by numeral 12 and detectors are indicated by numeral 14. The lines shown between the sources and detectors are the available source-detector measurement pairs, which are configured only as nearest neighbor optode pairs.
Referring now to FIG. 2, illustrating a sparse optode grid is generally indicated by numeral 20 in which the sources are indicated by numeral 24 and the receptors are indicated by numeral 26. The recreated simulated image is generally indicated by numeral 30 where the simulated reconstructed image for analysis is indicated by numeral 32.
The most extensively utilized NIRS brain imaging machine is restricted to first (1st) nearest neighbor measurements only and topography, e.g., HITACHI® ETG-100 OT and ETG-400 OT, although high frame rates can be achieved. The type of system and the use of the nearest neighbor optode pairs have limited lateral resolution and no depth-sectioning capabilities. Simulations indicate that increasing the density of the optode arrays can improve resolution, localization and cerebral signal discrimination. However high density optode grids place stringent requirements upon the dynamic range, crosstalk, channel count and bandwidth performance specifications of the instrumentation, and these challenges are unmet by previous systems.
FIG. 3 illustrates a rudimentary flowchart of a prior art source detector multiplexing system, which is generally indicated by numeral 100. Typically an analog input and output device indicated by 110 is connected to analog sources 112 which are then multiplexed 114, typically time encoding of the signal, into different source optode locations provided through a plurality of connectors 115 to the measurement subject, e.g., human user, 116. After interacting with the measurement subject, e.g., human user, 116, the detector multiplexing system 118 decodes the time coding via light conductors 117, e.g., fiber optic cables. The light is then received by the detectors 120 and preprocessed in the gain stages 122 and then stored. The signal is converted to a digital signal through the analog digital converter 124. All of the illustrated stages 110, 112, 114, 118, 120, 122 and 124 take into account any change in encoding strategy or optode grid design.
A typical detector system is indicated by numeral 130 in FIG. 4. Light 131 is received in a series of channels 132 through a plurality of detectors 133, e.g., silicon photo diodes (“SiPD”) that are connected to a programmable gain stage 134. After the first gain stage 134, there are a plurality of lock-in stages generally indicated by numeral 140. A lock-in frequency is a type of amplifier that can extract a signal with a known carrier wave from a noisy environment. There are represented a first lock-in frequency amplifier 142 and a second lock-in-frequency amplifier 144 for extracting at least two separate frequencies. The signals, after passing through programmable gain arrays 145, are then sent to sampling and hold stages 146. These digital signals are then provided to a processor 148. Therefore, there are significant issues when it comes to multiplexing as well as other significant issues involving both dynamic range and crosstalk. The present invention is directed to overcoming one or more of the problems set forth above.